1. Field of Invention
The invention disclosed herein generally relates to methods and systems for user guided automatic exposure control. More specifically, the invention disclosed herein relates to methods and systems for allowing a user to control the order and amount by which exposure related image capture settings in an image capture device are changed when exposure is to be increased.
2. Description of Related Art
Image capture devices exist both in analog forms and in digital forms. Analog image capture devices generally use film as a pickup, while digital image capture devices generally use an image sensor as a pickup. Analog image capture devices using film can be loaded with various “speeds” of film, typically expressed in terms of the ISO (International Organization for Standardization) value of the film. Typically, slower film, that is film with a lower ISO number, will provide a higher resolution image capture. Faster film, that is film with a higher ISO number, by contrast, allows images to be captured at higher shutter speeds or in lower light conditions, but at the cost of image resolution or quality, often with the addition of grain in the image. Digital image capture devices generally use digital pickups rather than film. Examples of digital pickups include charged-coupled devices (CCDs), complementary metal-oxide-semiconductor (CMOS) sensors, or other suitable semiconductor devices that capture an optical image from a lens system and convert it into an electronic representation of that image.
In order for an image capture device to appropriately record images, the pickup, be it analog or digital, has to be exposed to a sufficient quantities and qualities of light. Image capture devices tend to have three primary factors that determine the amount and quality of light to which a pickup is exposed and the effect of that exposure. These are aperture, shutter speed, and ISO. The aperture is the opening in the lens through which light is allowed to travel en route to the pickup. The aperture is often controlled by a diaphragm that controls the effective diameter of a lens opening. A lens aperture is usually specified by an f-number, which represents the ratio of the focal length to the effective capture diameter. Typical f-numbers for lenses for image capture devices include 1.4, 2.0, 2.8, 4.0, 5.6, 8.0, 11.0, and 16.0. Other f-numbers can exist on both ends of this exemplary range (f-1.0 and f-22.0 for example), as well as inside this exemplary range (f-6.3 for example). A lower f-number denotes a greater aperture opening which allows more light to reach the pickup. The shutter speed represents the time that the shutter of an image capture device remains open while the device captures images. While ISO does not affect the amount of light to which a pickup is exposed, it does affect the sensitivity of the pickup to light.
Each of the above three main image capture settings has properties that affect the image capture when the respective setting is changed. Increasing the f-number, which reduces the aperture size, increases the depth of field. The depth of field describes the extent to which subject matter lying closer than or farther from the actual plane of focus appears to be in focus. Changes in the shutter speed alter the way movement appears in capture images. For example, very short shutter speeds can be used to freeze fast-moving subjects, while very long shutter speeds can be used to intentionally blur a moving subject. Changes in the ISO also affect the image capture. Higher ISO numbers mean that the pickup is more sensitive to light, but they also cause coarser film grain or higher image noise.